NMR spectroscopy is an efficient method of instrumental analysis. In this process, HF pulses are radiated into an analysis sample, which is located in a strong, static magnetic field, and the HF reaction of the analysis sample is measured. Thereupon, the information is obtained integrally over a specific region of the analysis sample, the so-called active volume. The analysis sample generally consists of a cylindrical sample tube that contains the measurement substance to be studied, in solid or liquid form. The sample tube is typically located in a spinner. The sample tube and the spinner are transported into the NMR probe head from outside the magnet, using a transport system. When the sample tube is in the measuring position, the spinner is inside the turbine. The turbine allows the sample tube to rotate. In the measuring position, the sample tube is surrounded by one or more NMR coils. The innermost NMR coil has an inside diameter that is larger than the outside diameter of the analysis sample by as little as possible, since the bulk factor, and thus the sensitivity, of the NMR coil is dependent on the inside diameter and decreases as the inside diameter increases.
A HF seal is used to electrically “seal off” the HF network. However, if this HF seal is to be placed relatively high on the NMR probe head, almost the entire shielding tube has to be moved over this seal. This process can lead, inter alia, to damage to the seal. Moreover, a relatively large force is required to mount or dismantle the shielding tube, which can again cause damage to the seal and to the HF structure. In addition to the HF-tightness, a good electrical earthing contact is also desired.
When mounting the shielding tube according to the prior art, said tube brushes over the HF seal. This generates a relatively large force in the axial (mounting) direction. This force and the edges of the components can therefore destroy the HF seal due to high friction and resulting shearing.
In the concept of the so-called “SmartProbe” in company publication “HF immunity modifications” by Bruker BioSpin AG, Industriestrasse 26, CH-8117 Fallanden, Switzerland, dated 2007) currently used in the prior art, the HF seal is positioned at the bottom of the base disc. In a more recent concept, the so-called iProbe, this seal is positioned at the halfway point for conceptual reasons. When the HF sealing concept remains the same, when mounting the shielding tube in the case of the iProbe, an HF seal would probably, if not certainly, be destroyed, since the shielding tube brushes over the seal across a very long stretch. In addition, the high forces in production cannot be controlled so precisely for mounting not to cause any damage to other components.